Straightening out a fork is more art than mechanics, and you'll find very few shops if any these days that will straighten out a fork. You may have them help order you a new fork.

A fork needs to be aligned over a number of dimensions.

First is to insure that the forkends are separated a standard distance for the front axle spacing. Most modern front axles have 100mm spacing. Easiest way to do this is lay the fork against a non-abrasive surface, and either push down on the other arm carefully, or pull firmly while having someone else stepping on the bottom fork blade until you sense a tiny amount of yield. Measure again and repeat if necessary. Better to bend a little at a time than to try and get it right on the first shot and overshoot.

Second, the forkends must be aligned parallel to the level of the fork crown. The easiest way is to have a fork alignment jig that will secure the forkends in something like a quick release axle. But this must be a very strong clamp and the clamp must not flex from side to side. The other option is to find something like the gap under a heavy duty door. You can also sandwich the fork tips between block of wood and some steps/stairway to a porch for example. Anything than can hold the fork tips and prevent side-to-side twist. Next, take a steel bar wrapped in tape (to protect paint on the fork) or 2x4 wood stud about 4 - 6 ft long. Slide the bar or stud under the blade that needs to come up (peek down the steerer), and over the other fork blade. Pry firmly and gently. Remove, check alignment (place on flat surface and look from side, or if the fork tips are level, measure the blades for level near the crown.

Third, with forkends bottomed out, the steerer should be centered on the mid-line that bisects the fork. You will need some sacrificial headset or mechanism that goes over the steerer and protects the tube from ovalizing or thread damage while we apply lateral force on that fork. Ideally, you'll have an alignment table with level fork attachment mechanism that is VERY SECURE. Holding the forkends in the clamp, and using a long cheater tube over the steerer and protection mechanism, pull on the steerer tube sideways until it centers on the mid-line.

Lastly, the fork curvature or offset angle at the crown should be set to achieve the intended trail. This is best done with a rounded block of wood under the fork that is high enough to raise the fork off the table. Usually, the fork is laid concave down on the rounded surface and force applied to the fork crown and upper fork blades. For straight blade forks, a straight block of wood the same height as the fork tip mount will work and force applied to the steerer tube.

This only works for steel forks. Don't try it on aluminum or CF forks and never on fork with some type of epoxy bonded steerer.